PWM Strategies for Common-Mode Voltage Reduction in Current Source Drives

The common-mode voltage (CMV) in the motor drive system could damage the motor insulation and induce destructive bearing current. Various reduced CMV space vector modulation (RCMV SVM) methods have been proposed in both voltage source converter (VSC) and current source converter systems. Most of them reduce the CMV by avoiding the use of zero-state vectors. Recently, a zero-state vector selection strategy for CMV reduction in CSCs has been proposed, which allows the use of zero-state vectors and achieves reduced CMV without affecting the modulation index range and the harmonics performance of converters. This paper further investigates three possible zero-state vector selection strategies in RCMV SVM for current source drives where the PWM CSR and CSI are connected back to back. Among the three methods, Method 1 and Method 2 are suitable for CMV peak value minimization, while Method 3 is proposed for the average CMV reduction. These methods can then be considered for different types of drives (with or without isolation transformer) to reduce the insulation stress or to limit the resonance in the common mode circuit. Details of the three zero-state vectors selection methods are presented. Both simulation and experimental results are provided to verify their effectiveness.